Bug 932793 - Intermittent test "thread_ui.js > scrolling scroll 100px, should be detected as a manual scroll" r=schung

* Fix intermittent scripts by sending the scroll event in the test
* Fix bad tests that were revealed in the process: `done` callback set on the
  suite function instead of the test function, wrong SMS messages.
* Linearized and de-asynchronized some tests
Merge pull request #14483 from julienw/932793-intermittent-scroll-tests

Bug 932793 - Intermittent test "thread_ui.js > scrolling scroll 100px, s...